MMP is an intermediate for the manufacture of both d, 1-methionine and 2-hydroxy-4-(methylthio)butanoic acid ("HMBA"). Methionine is an essential amino acid in which components of the animal feed compositions are commonly deficient. HMBA provides a source of methionine, and is widely used as a methionine supplement in animal feed formulations. MMP relatively free of impurities is typically required for the manufacture of HMBA or methionine.
MMP is conventionally produced by the reaction of acrolein with methyl mercaptan. In a conventional process for the preparation of MMP, acrolein and methyl mercaptan are introduced in a liquid phase into a reactor containing liquid-phase MMP product. The reaction takes place batchwise in the liquid phase. In order to produce MMP of the quality typically desired, refined acrolein is typically used in the manufacture of HMBA and methionine.
Acrolein is a highly toxic and flammable material. It is conventionally produced by the vapor-phase oxidation of propylene over a solid-phase catalyst, producing a crude, gaseous reaction product which contains acrolein, water vapor, acrylic acid, acetaldehyde, and other organic by-products. Typically, the gas is treated to remove acrylic acid, then contacted with cooled water for absorption of the acrolein. The resultant aqueous solution is distilled to recover the absorbed acrolein and other organic components. The crude acrolein is then refined to reject lower-boiling impurities such as, for example, acetaldehyde, producing a purified, liquid acrolein product. Since the conventional processes typically use a batch reaction system, condensation and in-process storage of liquid acrolein is necessary as a surge buffer between the acrolein process and the MMP reactor.
Storage of liquid acrolein involves significant toxicity, fire and explosion hazards. High capital and operating costs are consequently incurred in providing for the safe handling of acrolein. Substantial enhancements in the safety of handling acrolein would be achieved if acrolein were transferred directly and continuously from the acrolein manufacturing process to the MMP reactor without intermediate storage. Since the conventional, commercial processes for the preparation of MMP involve liquid-phase reactions, the need to condense the gaseous acrolein product has been considered unavoidable. However, further enhancements in the safety of handling acrolein and the process efficiency of manufacturing MMP could be achieved if the acrolein were transferred to the MMP reactor in the vapor phase, i.e., without significant condensation of the acrolein.